大型水轮发电机定子中性点高阻接地暂态分析

为准确分析计算发电机间歇弧光过电压以及单相接地故障电流,提出了采用准分布电容参数的定子单相接地多回路模型.该模型可以比较准确地计及气隙磁场谐波及定子分布电容的影响.对三峡左岸电厂一台大型水轮发电机进行了分析计算,结果表明,发电机中性点采用高阻接地方式下,定子绕组发生单相接地时,若取较高的中性点接地电阻则对减小故障电流的作用较有限,且会带来比较大的暂态过电压;综合考虑接地故障电流和暂态过电压,则中性点接地电阻宜取2～3倍的中性点对地等值容抗;若发电机频率发生偏移,则有可能出现较大的暂态过电压.

TRANSIENT ANALYSIS ON LARGE HYDRO-GENERATOR WITH HIGH RESISTANCE GROUNDING

To calculate and analyze the transient over-voltages and the fault current accurately during the stator intermittent arc grounding, a multi-loop model with quasi-distributed capacitances is presented with which the influence of the distributed capacitances and the harmonic magnetic field in air gap can be more accurately taken into account. On this basis the calculation for a large hydro-generator in the Three Gorges Power Station is carried out and the calculation results show that when single phase to ground fault occurs in stator winding under the high resistance grounding of the generator neutral and the value of neutral resistance is high, only finite fault current can be reduced, and a higher transient over-voltage may occur. When the fault current and the transient over-voltage are synthetically considered, it may be proper that the value of neutral resistance should be 2 to 3 times of that of neutral point equivalent capacitive reactance. If the frequency of the generator deviate from its normal value, the higher transient over-voltage may occur.